Wright Stuff B

[a.novak]

Thank you! Two years ago in the event elastic launched gliders I used a box similar to that design for transporting, but of course it was much smaller than the wright stuff planes. This really helps thank you

[jgrischow1]

Jgri,

Did removing 6" from the tailboom and moving the clay ballast cause the CG to be about 1.75" - 1.875" forward of the wing TE? If so, after setting the wing incidence to about 1/4", and the other trim settings per my earlier post, and winding the rubber fully (and backing off enough turns to keep off the ceiling), hopefully you'll be seeing flights in the 2:00 to 2:30 range.

Good luck. Be sure to post any other questions you might have.

Brian T.

Thank you.

We finally got some chances to run some tests. With your recommended settings, my kids could not get the plane to fly stable. However, after moving the wing forward an inch or so, it seemed to correct the issue. The CG is now only slightly in front of the TE, though, no where near 1.75 inches.

Our incidence is also more than 1/4 inches, and has always been (even with our old configuration). Not sure why, but the plane never seemed to climb unless it was 5/16 or more.

In any case, after seemingly getting it to fly in a stable manner, we had some interesting issues. At times, the plane would still fly in the manner I described pre-changes: it starts to climb and then descends after a half turn or so and hits the ground. However, this time it is only happening with a decent amount of torque. With less torque, this isn't an issue. Unfortunately, my kids have not recorded any torque data this week, so I only have visually observations to go by, but let me try to explain what I mean: We will launch the plane with, say, 1000 turns of .065, backed off 25. It does the half turn/go to ground thing. We then pick the plane up and re-launch it with remaining turns, no re-winding or anything, and it flies nice and stable for 45 more seconds. Not sure what's going on, but I've seen this several times, and it seems there is a relationship between launch torque and it flying erratically like this.

We have had another issue since re-configuration: At times, it will fly fine for a few turns, and then just suddenly stop turning, and fly straight into a wall. This didn't seem to happen pre-configuration.

Again, both of these issues only happen sometimes.

One more thing I just realized: our plane has no washin. It didn't before and it doesn't now. Would it help if they added some, should they add some, and how would they to an already built plane? Break the wing?

Thanks for all the help.

[coachchuckaahs]

The behavior sounds to me like too much torque or lack of stability. 50 unwinds may not be enough, depending on the prop you are using. We saw this behavior last year with the cut down Ikara non-flaring prop.

We are typically unwinding to about 0.2-0.25 oz-in this year. 50 unwinds on full rubber does not seem to be enough. We are using somewhat thinner rubber than that (maybe 0.056", or 0.372g/in), and that will wind somewhere around 3000 turns, and then unwind perhaps 200-250 turns. With your thicker rubber, its at even higher torque.

Just guessing, your rubber can probably take in the neighborhood of 2000 turns, and then back off at least 200 turns. Be sure to lube, and to stretch to about 7X nominal length. Wind about half at full stretch, then start walking in.

Can you describe the stability issues you had with the forward CG? By moving the wing forward, you reduce stability (moved CG back relative to the wing). SO maybe describe the stability issue you saw with the forward CG. Did you increase incidence until you got a stall on letdown, then decrease a little?

Your incidence would indicate a decent CG, unless you also have stab positive incidence. We are running 0 on the stab, about 9-10mm on the wing.

Coach Chuck

[bjt4888]

Jgri,

Yes, most likely you need about 1/16" to 1/8" of left wing washin to prevent rolling to the floor during the initial high-power portion of the climb. Yes, partially cut through the left LE spar near the wing mid point and gently crack and hold about twice as much washing as you want and apply a drop of CA. Hold for about 90 seconds (if fresh CA) and the spar will partially return to where it was and you will have a starting point for washin.

Agree with Chuck that a detailed description of what you are observing when the CG is set to 1.875" forward of the wing TE.

Winding to 90% full turns measuring max torque (should be about .8 or .85 in oz) and backing off to a reasonable launch torque (initially .25 in oz) are critical steps to testing. Winding to 1,000 turns and backing off 50 is massively underwinding and then significantly short of the correct backoff turns (depending upon the length of the 1/16" motor). It is possible that the winding they are currently doing is resulting in a launch torque in the .35 to .45 in oz range ( based upon our test results) and, without left wing washing, this much torque can easily result in a banking turn to the floor.

How much left wing offset, stab tilt, tailboom offset and thrustline offset does your airplane have?

Brian T

[bjt4888]

Jgri,

One more note on cracking LE to add washin; make partial cut through at a shallow angle relative to the spar lengthwise direction. The resulting scarf joint will be pretty strong.

Brian T

[coachchuckaahs]

Before cutting your LE, it will be important to observe the character of the "dive". If the inboard wing is tilting downward in the circle significantly, then you may need to add wash-in. If the plane simply goes down, look at your static stability, as well as your launch torque. A launch torque of 0.20 to 0.25, as Brian notes, is a good starting point, especially with a non-flaring prop. If your static stability is off, you can chase a LOT of adjustments (including wash-in) and still have the same symptoms. Get the plane working on low torque, then observe higher torque for further adjustments.

Unlike last year, we have ended up with very little wash-in on this year's plane. Of course, the amount needed may heavily depend on the plane's design and imperfections.

Depending on how your wing posts are mounted to the wing, you may be able to remove the wing post mount (cut it off), impose a slight tilt to the LE or TE, and re-glue the wing post. On some designs, this maybe easier than cutting and splicing the spar/LE/TE, but on other designs it may be harder. We have carbon LE, so this is the only approach we can use.

When any change is made, including wash-in, rudder, tail tilt, etc, be sure to re-trim the plane for smooth let down. Add incidence until stall just starts in letdown, then remove a mm or so. Almost any adjustment you can make to the airframe will require re-testing. We use 400-600 winds without any unwinds for our test rubber. this will climb a little, and then begin letwon where you observe for stalling.

Coach Chuck

[bjt4888]

Yes, I'm in full agreement, static stability first, fly and observe, then determine if and how much washin might be needed.

[waffletree]

Does anyone have a picture of or know the size of the wright stuff gym at PA states?

[jgrischow1]

The behavior sounds to me like too much torque or lack of stability. 50 unwinds may not be enough, depending on the prop you are using. We saw this behavior last year with the cut down Ikara non-flaring prop.

We are typically unwinding to about 0.2-0.25 oz-in this year. 50 unwinds on full rubber does not seem to be enough. We are using somewhat thinner rubber than that (maybe 0.056", or 0.372g/in), and that will wind somewhere around 3000 turns, and then unwind perhaps 200-250 turns. With your thicker rubber, its at even higher torque.

Just guessing, your rubber can probably take in the neighborhood of 2000 turns, and then back off at least 200 turns. Be sure to lube, and to stretch to about 7X nominal length. Wind about half at full stretch, then start walking in.

Can you describe the stability issues you had with the forward CG? By moving the wing forward, you reduce stability (moved CG back relative to the wing). SO maybe describe the stability issue you saw with the forward CG. Did you increase incidence until you got a stall on letdown, then decrease a little?

Your incidence would indicate a decent CG, unless you also have stab positive incidence. We are running 0 on the stab, about 9-10mm on the wing.

Coach Chuck

I'm sorry but I don't remember the details...when they tried to fly with that CG it just wouldn't climb...so one of my kids just moved the wing up until it started to climb normally.

Jgri,

Yes, most likely you need about 1/16" to 1/8" of left wing washin to prevent rolling to the floor during the initial high-power portion of the climb. Yes, partially cut through the left LE spar near the wing mid point and gently crack and hold about twice as much washing as you want and apply a drop of CA. Hold for about 90 seconds (if fresh CA) and the spar will partially return to where it was and you will have a starting point for washin.

Agree with Chuck that a detailed description of what you are observing when the CG is set to 1.875" forward of the wing TE.

Winding to 90% full turns measuring max torque (should be about .8 or .85 in oz) and backing off to a reasonable launch torque (initially .25 in oz) are critical steps to testing. Winding to 1,000 turns and backing off 50 is massively underwinding and then significantly short of the correct backoff turns (depending upon the length of the 1/16" motor). It is possible that the winding they are currently doing is resulting in a launch torque in the .35 to .45 in oz range ( based upon our test results) and, without left wing washing, this much torque can easily result in a banking turn to the floor.

How much left wing offset, stab tilt, tailboom offset and thrustline offset does your airplane have?

Brian T

1,000 winds wasn't our max...we were just doing different winds/torque to check if it was flying stably with the new settings. We usually start at about 300 winds and go up from there. My impression was winding a lot when you don't know if your plane will fly or not is not a good use of time. I will suggest to them about the torque stats you mentioned.

I will measure the stats you requested tomorrow.

Jgri,

One more note on cracking LE to add washin; make partial cut through at a shallow angle relative to the spar lengthwise direction. The resulting scarf joint will be pretty strong.

Brian T

OK, thanks.

Before cutting your LE, it will be important to observe the character of the "dive". If the inboard wing is tilting downward in the circle significantly, then you may need to add wash-in. If the plane simply goes down, look at your static stability, as well as your launch torque. A launch torque of 0.20 to 0.25, as Brian notes, is a good starting point, especially with a non-flaring prop. If your static stability is off, you can chase a LOT of adjustments (including wash-in) and still have the same symptoms. Get the plane working on low torque, then observe higher torque for further adjustments.

Unlike last year, we have ended up with very little wash-in on this year's plane. Of course, the amount needed may heavily depend on the plane's design and imperfections.

Depending on how your wing posts are mounted to the wing, you may be able to remove the wing post mount (cut it off), impose a slight tilt to the LE or TE, and re-glue the wing post. On some designs, this maybe easier than cutting and splicing the spar/LE/TE, but on other designs it may be harder. We have carbon LE, so this is the only approach we can use.

When any change is made, including wash-in, rudder, tail tilt, etc, be sure to re-trim the plane for smooth let down. Add incidence until stall just starts in letdown, then remove a mm or so. Almost any adjustment you can make to the airframe will require re-testing. We use 400-600 winds without any unwinds for our test rubber. this will climb a little, and then begin letwon where you observe for stalling.

Coach Chuck

Thanks for the tips.

[jgrischow1]

Jgri,

Yes, most likely you need about 1/16" to 1/8" of left wing washin to prevent rolling to the floor during the initial high-power portion of the climb. Yes, partially cut through the left LE spar near the wing mid point and gently crack and hold about twice as much washing as you want and apply a drop of CA. Hold for about 90 seconds (if fresh CA) and the spar will partially return to where it was and you will have a starting point for washin.

Agree with Chuck that a detailed description of what you are observing when the CG is set to 1.875" forward of the wing TE.

Winding to 90% full turns measuring max torque (should be about .8 or .85 in oz) and backing off to a reasonable launch torque (initially .25 in oz) are critical steps to testing. Winding to 1,000 turns and backing off 50 is massively underwinding and then significantly short of the correct backoff turns (depending upon the length of the 1/16" motor). It is possible that the winding they are currently doing is resulting in a launch torque in the .35 to .45 in oz range ( based upon our test results) and, without left wing washing, this much torque can easily result in a banking turn to the floor.

How much left wing offset, stab tilt, tailboom offset and thrustline offset does your airplane have?

Brian T

Not positive what left wing offset means. Both sides of the wing are the same length and are the same angle of dihedral. The wingposts are attached on the left side of the fuselage.

Not a whole lot of stab tilt that I can detect. However, before concluding that that (or the lack of wing offset) is why our plane isn't turning after a few turns, I must say that it was turning fine before. I do seem to recall our model last year (based on FFM from HS 2016) had a longer left side of wing and a decent amout of stab tilt, and this has neither, but I promise it turned fine the entire flight until recently. I think once we started having these issues one of my kiddos put a small amount of clay on the left wing to try to bank it more.

Tail boom offset seems to be a few degrees max. Hard to measure.

Pardon my ignorance, but does thrustline offset mean relationship of prop axis to fuselage? If so, 3 degrees is what the kids say they did.

Sorry I'm not more helpful in describing our issues or providing stats. Sometimes I feel like a patient who can't describe his symptoms to the doctor.